Dufour Owners Association: new forum reply to Quick Hot Water Calorifier PRV

New reply from Graham Marks

<p>I had the very same problem on my 425GL, after a lot of research I have solved the problem, there are two different problems here, the leaking pressure relief valve (PRV) on the calorifier and a water pump that cycles when the tap is opened. The cycling water pump problem only occurs if you have a pressure switch controlled pump, this can be cured by fitting an expansion vessel in the cold water side of the system just after the pump, if you have as in my case a variable speed electronic pump then there is no need to fit an expansion vessel as the pump performs the same function.</p>
<p>The leak from the PRV on the calorifier when running under engine is caused by the fact that the hot water system is maintained at pump pressure however the engine adding heat to the calorifier has the effect of increasing the pressure further and causing the PRV to lift to release it. The solution to this is to fit an expansion vessel to the hot water side of the system to absorb the excess pressure, it has to be fitted here as the PRV has a non return valve fitted within therefore if it is fitted in the cold water system it will not absorb the excess pressure in the hot water system, the pressure increase only occurs after the PRV. My solution to this was to unscrew the PRV from the calorifier and insert a tee piece onto the boiler then re-fit the PRV onto that tee piece, I then connected an expansion vessel to the tee.</p>


Original Post by Matthew Dellar

Quick Hot Water Calorifier PRV

<p>Hi </p>
<p>Can anyone help with advice on a Quick hot water calorifier? </p>
<p>I seem to be getting a small amount of water leaking from the pressure release valve on the Calorifier after running the engine. I have swapped the PRV for a new one but this didn't make any difference.</p>
<p>Has anyone had this problem or can advise on what could be wrong and how to fix?</p>
<p>Thanks, Matt.</p>